This invention relates to the preparation of P,P-dihydrocarbylphosphinoacetic acids, which are useful as intermediates in the preparation of ethylene oligomerization catalysts. In one particular aspect, this invention relates to the preparation of P,P-diarylphosphinoacetic acid. In another particular aspect, this invention relates to the preparation of P,P-dialkylphosphinoacetic acids. In a further particular aspect, this invention relates to the preparation of P,P-dicycloalkylphosphinoacetic acids.
P,P-disubstituted phosphinoacetic acids of the type R.sub.2 P--CH.sub.2 --CO.sub.2 H are known, and their preparation has been described in Chemische Berichte 93, 1960, pages 803-808. The preparation method described in this article comprises the steps of reacting a dihydrocarbyl-substituted alkali metal phosphide, e.g., KP(C.sub.6 H.sub.5).sub.2, with a haloacetate, e.g., ethyl chloroacetate, and hydrolyzing the formed dihydrocarbylphosphinoacetatic acid ester with an alcoholic sodium hydroxide solution and thereafter with sulfuric acid. This prior art synthesis requires the use of very reactive alkali metal phosphides. The present invention is directed to a less dangerous, more practical synthesis of P,P-dihydrocarbylphosphinoacetic acids which does not involve the use of alkali metal phosphides.